If you choose to help him, he will give you the name "AmShaegaar" and will tell you some things about the world of Arx and the Guild of Travellers. He will also help you kill the Lord Goblin at the end of The Catacombs map. At this point, you can give him a bone or a dagger and he will equip it. You can heal him by using a Life Potion on him.

If you choose NOT to help him, when you break the Wooden Grid from the cell, he will say your name AmShaegaar, but will leave the player in an ambiguity state, since the player will never know if that is his real name and if so, if he ever knew Kultar before the black out. He will not help you kill the Goblin Lord thus having to kill him by yourself.

During the "Save the Kingdom" quest the player is knocked off by an Ylside. The Ylside is Kultar himself. Based on the player's early decisions, this reunion has two different outputs:

If you helped him escape from the Goblin Prison he will tell the player how Iserbius approached him and told him about his plans to reincarnate Akbaa into Arx with the intention to "bring the Sun back to Arx". When he sees AmShaegaar again he realises that it was all a mistake. He takes off his Ylside armor (which you can take) and helps the player escape the castle through a trapdor.

If you DIDN'T help him escape he will attack, therefore the player has to kill Kultar. Also, Ylside Armor won't be available untill later in game.